Furnace structure for reducing ores



pt. 30, 1 E. w. DAVIS 2,257,110

FURNACE STRUCTURE FOR REDUCING ORES Filed April 3, 1940 9 Sheets-Shet 1 f N VE-NTOE EDWARD W. DA V/d' ATroe/vsvgs v p 30,1941- E. w. DAVIS 2,257,110

FURNACE STRUCTURE FOR REDUCING ORES Filed April 5, 1940 9 Sheets-Sheet 2 AL) 6 .[NVENTOE 5" EDWARD 0A V16 ATTORNEY:

P 30, 1941} v E. w. DAVIS 2,257,110.

FURNACE STRUCTURE FOR REDUCING ORES Filed April 5, 1940 9 Sheets-Sheet 3 3 FM? Y 'ATT RNEYu' p 9, 1941- E. w. DAVIS 2,257,110

- FURNACE STRUCTURE FOR REDUCING ORES Filed .April 3, 1940 9 Sheets-Sheet 4 i i I Q a w 4 37 I i /es [NVENTOR E0 WARD W DA v1.5

141- TQENE Yr p 1941- I E. w. DAVIS 2,257,110

FURNACE STRUCTURE FOR REDUCING ORES Filed April 3, 1940 9 Sheets-Sheet 5 9 MWWW 14 TTORNA'YJ Sept. 30, 1941. E. w. DAVIS FURNACE STRUCTURE FOR REDUCING ORES Filed April 3, 1940 .9 Sheets-Sheet 6 v 6 1 6 6 9 0 Y TV m NA 2 F w w n M L 5 h mfl mp r G- A I m H W @m E o I 1 T m3 9 Q N "n .m W AWTQ w M P w ,rP e H 0 9 a 7 G p 30 1941. E. w. DAVIS 2,257,110

FURNACE STRUCTURE FOR REDUCING ORES Filed April 3, 1940 9 Sheets-Sheet 7 j N VENTOE EDWARD W DA llr'r klvgvs p 30, 1941- E. w. DAVIS 2,257,110

FURNACE STRUCTURE FOR REDUCING ORES Filed April 3, 1940 9 Sheets-Sheet 8 I I III II II 'JUIIII rHlIHllil l i- HI n n I! I 1 in A N Y [NVENTOE o2 4 96 950 I000 I020 1040 106 105 FDWAED W D/IV/J Te peratu e 6 g? PM,

Sept. 30, 1941- E. w. DAVIS FURNACE STRUCTURE FOR REDUCING ORES Filed April 3, 1940 9 Sheets-Sheet 9 .ZI-VVENTOE 50 WA 20 W DA 1/16 a M 0m Wm Patented Seph 30, 1941 UNITED STATES PATENT OFFICE FURNACE STRUCTURE FOR REDUCING ORES Edward W. Davis, Minneapolis, Minn., assignor to Regents of The University of Minnesota, Minneapolis, Minn., a corporation of Minnesota Application April 3, 1940, Serial No. 327,653

12 Claims.

' as gangue.

An object is to provide an apparatus in which large tonages of hematite may be converted to magnetite at a minimum cost.

Among other objects of the invention are to provide a furnace of the shaft type in which the ore is fed into the top of the shaft, and in which the shaft is kept filled with ore; to provide a single means for regulating the speed of down travel of the material being treated; and to provide means whereby uniform heating of the material and application of the reducing fuel thereto is obtained. whereby uniform mixing is obtained during heating and to attain both objects without I channeling of-the material.

It is another object of the invention to provide an apparatus in which the coarse and fine ore are handled separately to obtain proper heat interchange, and then mixed as the ore passesthrough the reduction zone. It is also an object of the invention to provide a furnace structure in which the coarse and fine ores are mixed so as to obtain good heat interchange without allow ing channeling to occur in the ore.

It is also an object of the invention to providea furnace structure in which coarse and fine ores are separately handled and then intermixed by static devices as the ore passes thereover.

It is a specific object to provide such a furnace structure in which the mixing is'accomplished by baffles of long life.

Other features relate to the design and placement of the bailles; the manner of controlling the entry of the coarse material into the heating zone so as to prevent rolling and therefore maintain a solid unbroken column of down-moving material; the use of means for removal of unconsumed gas below the bailies in the reduction chamber to prevent its entry into the heating zone; the use of water for quenching or cooling the reduced ore, and the utilization of steam produced by quenching for vaporizing fuel oil for reduction purposes.

Objects, features and advantages of the invention will be set forth in the description of the drawings forming part of this application, and in said drawings trating the general construction of the furnace;

Figure 2 is a vertical section illustrating the hopper details and theconstruction at the upper part of the furnace;

Figure 3 is a view complemental to Figure 2,

illustrating the lower portion of the furnace;

Figure 4 is a section illustrating the lower part of the furnace, and taken approximately on line of Figur Figure 5 is a sectional view of the upper part of thefurnace taken approximately on line 5-5 of Figure 2;

Figure 6 is a detail vertical section further illustrating the hanger construction for the exhaust and hot ports;

Figure 7 is a vertical section on line i-'| of Figure 6;

Figure 8 is a plan section taken approximately on line 88 of Figure 2;

Figure 9 is a vertical section of the suction box taken approximately on line 9-9 of Figure 2; Figure 10is a horizontal section through the hot ports taken approximately on line Ill-l0 of Figure 2; Figure 11 is a vertical section through the'oil vaporizer, and water condensing apparatus;

Figure 12 is a plan of the quenching tank feeder plate and conveyor assembly;

Figure 13 is a diagrammatic vertical section illustrating the operation and process;

Figure 14 is a diagrammatic section on line ll-H of Figure 13 illustrating the up-flow of the gases and down-flow of the material;

Figure 15 is a diagram showing the effect of moisture in the ore, on furnace capacity and oil consumption; and

Figure 16 is a diagram showing the relation between steam temperature and roasting efficiency.

General scheme Referring first to Figure 1, the device has an iron frame generally indicated at I, which includes cross beams generally indicated at 2 which support a masonry structure generally indicated at 3, said masonry structure providing a vertical shaft or chamber shown in dotted lines and gen-.

erally indicated at 5. The ore is prepared for reduction andis reduced, .as itmoves continuously downwardly. Mounted above the structure 3 are hopper structures comprising upper and lower sections respectively generally indicated by numerals 6, 1. The lower section I is supported by cross beams 8 and the upper section 6 is supported by cross beams 9 and Ill. Thelower ter- Figure 1 is an elevation partly in section illusminals of section 6 and the upper terminals of or chamber of themasonry structure for the same purpose. By this means the masonry structure can expand and contract independently I of the hopper section and each hopper section can expand and contract independently of the other. The hopper section 1 extends into the shaft 5 and has structures later to be described, which are hung from or in part supported thereby.

The furnace proper as constituted by the masonry structure 3 consists of two main zones; a heating zone generally indicated at l2, and a reducing zone generally indicated at I3, said zones being continued toform a shaft generally indicated at 5. Below the reducing zone there is provided a cooling zone generally indicated at M, which is later described in detail. r

The travel of the gases for heating and the travelv of the gases for reduction is upwardly in each instance and is controlled by suction. The heating gases travel upwardlyv as the charge moves downwardly and are drawn out of the furnace by an' exhaust fan indicated at l6, which delivers into pipe l1, and which has its suction side connected by a suitable pipe 2|, with a suction box or dust catcher indicated at 22. This box 22 is connected by a manifold 23, and a series of pipes 24, see Figure 8,- with a series of tubular exhaust ports indicated at 25, which are open at the bottom and extend completely across the heating chamber or zone |2. Hot gases, which are the products of combustion from'a combustion chamber '26, are sucked through passages 21- into hot ports generally indicated at 26, thence from the tops of said ports upwardly through the charge passages 25. These hot drying and heating gases pass to the suction box or exhaust chamber 22.

The minimum temperature of the gas, leaving the exhaust ports v25, is determined by the amount of water in the ore and in the products of combustion that the gases must carry away .as vapor. The combustion chamber 26 is preferably designed for the combustion of fuel oil, but natural or artificial gas or pulverized coal may obviously be used. A thermo-couple 33 is used to ascertain the temperature in passages 21.

The mixing of fine ore with the coarse is an important feature, as a're'the means for obtain ing and maintaining the proper mix ratio between the coarse and fine ores, and for obtaining heat transfer from the coarse to the fine ore. These matters are treated in detail here below. f

. The rate of travel of the ore through the furnaceis controlled by feeder means, in this instance a rotary feeder plate 30, arranged in the cooling zone beneathwater in a quenching tank 3|, see Figures 3 and 4. This plate operates in a manner to be described in detail.

The gas for reducing-the ore, which may be natural gas, producer gas, or hydrocarbon vapors from hydrocarbon fuel oils, is introduced at the bottom of the furnace through pipe 32, see Figure 1, and then passes upwardly through the ore.

Where the gas is formed by vaporizing fuel oil this may be done in a vaporizer 35. The vaporizer may be heated by steam generated in the quenching tank. The steam which is generated by quenching the reduced ore rises into a chamber .36 and passes through pipe 31, to the top of the vaporizer 35. A thermo-couple 451s in the chamber l2 to exhaust.

\ used for indicating the temperature in the steam.

chamber. Water of condensation is returned to the quenching tank 3| in which the feeder plate 30 operates. The ore is discharged from the furnace and onto the plate through a tubular member 39.

In the apparatus 35, see Figure 11, are water sprays 40 which condense the steam after it has vaporized the oil, leaving in addition the noncondensable gases consisting of air which was in solution in the water and of hydrogen formed by chemical reaction in the quenching chamber. The quantities of these gases are small and they are drawn off through a pipe 4| and through an explosion trap 42. The opposite side of the trap is connected by a suction pipe 43, with the suction box 22, the suction-fan It thus serving to exhaust the gas through the trap. At the beginning of operation water is put into the explosion trap but with continuous use water of condensation increases the quantity of water and at intervals this water is drained out, the level being ascertained by a suitable water gauge.

Having given a general description of the scheme, I will now proceed to describe various structures in detail.

Hopper structure Referring to Figures 1, 2 5: For some operations the ore to be roasted is crushed to three- 54 of the hoppers 50, 5| enter corresponding" narrowed upward extensions 55, 56 of the lower hopper section 1.- The coarse ore is finally delivered into the reducing chamber l3, and is handled within that chamber in a manner to be described. The fine ore hopper or bin 52 delivers by means of a series oflnarrow spouts 60, see Figure 5, into a'receiving trough 6|, which trough in turn delivers into a corresponding number of tubes 63.. The lower ends of these tubes extend into the heating chamber l2, and deliver between plates which define a passage which leads the fine ore to a point near the bottom of the chamber where it is mixed with the coarse ore. By this means the finer -ore is delivered into the middle of the coarse ore which has passed downwardly into the chamber l2 to the bottom portion thereof.

Exhaust ports 7 Referring now to Figures 2, 5 and 8 and to the structure of what are herein called the exhaust ports. These ports, as previously mentioned, deliverto pipes 24 which in turn deliver to manifold 23. These ports are constituted by inverted U or V-shaped casings 20. These cas- Figures 7 and 8. The gases can also pass upwardly between the plates and through said openings III. The tops of the plates 86 are capped by a plate II to prevent upward escape of gases. Thus upwardly traveling drying and heating gases are baffled into the pipes 24 and manifold 23, by means of the suction created by fan I8 in the suction box or dust collector 22. It is noted that the plates 66 are supported at the ends by the walls of the lower hopper I.

Plates 68 support other plates, see Figures 2, and 7 which constitute a continuation of the fine ore passage, and into which the bottoms of the pipes 63 deliver, and by which passage of the fine material is delivered into the heating zone centrally of the mass of coarser ore. These plates are indicated by the numeral I5 and they are connected to the plates 56 by plates 14..

Hot ports These hanger plates I5 have openings I8.for receiving the inner endsof the pairs of hot port casings which receive hot gases from the combustion chamber 26, These hot ports 28 are composed by a. series of inverted U or V-shaped casings IS, the inner ends of which enter the openings 18 of the plates 15 and the outer ends of which are inserted (see Fig. 2) in openings I9 of the masonry. Referring to Figure 10, it will be seen that inspection passages 80 communicate with the interior of casings I6, openings 19 and passages 21, of the furnace.- The furnace operator is thus provided with an easy means of inspectingthe'interiors of these furnace parts.

The casings 16 are open at the top as at 82 and are provided with covers or cowls 83 so spaced that gas rising into the casings I6 escapes as shown by the arrows in Figures 5 and 14. The sides of the casings I8 are reenforced at the bottom by cross elements 85. The hot ports and all of the baflles are made of an alloy of iron, nickel and chromium, the exact proportion of the elements depending upon the service required. It is necessary to provide adequate means for expansion to prevent warping and buckling. To this end the inner ends of the casings 16 are spaced apart as in Figure 'I to allow for expansion, the outer ends of each element only being fixed in the masonry, see Figure 2. Expansion also has been provided for the exhaust ports 25,

by allowing space between the ends thereof and the elements and 61, by which they are supported.

From the coarse bins, the ore passing through the constrictions 53, 54, 55, and 56 is delivered into the enlarged lower portion of the lower hopper I. The purpose of this enlargement is to/ spread the orehorizontally. The angle of t e sides 88 of this hood to the horizontal is a t 60 which is greater than the angle of repos of the ore, and the ore is thus pressed against the surface of this hood at all times so that no li ning of the individual particles occurs. The ore next enters the heating chamber, the structures within which have been previously described.

The inner ends of the hot port casings I8 are spaced at III to allow for expansion. In order to make the hot port casings continuous across space, a detachable cowl is formed by plate members I12 having hook-like upper extremities I13, the outer ends of which engage the inner faces I'll of the casings l6. Thehorizontal dimension of these members I12 is less than the space be-' tween the plates. I5, to allow for expansion.

B ames Suspended fromthe hot ports 16 are two opposed series of superposed baflled elements. The outermost member of each series rests on an inclined surface 90 which surfaces lead inwardly and downwardly to the reducing chamber or zone 5. These baffles are respectively indicated Ill, 92, 93, and they are respectively connected to the elements as at 94.

Referring now to Figure 5, as well as to Figure 2, means is provided near the entry point of the finer ore, into the heating chamber, to regulate the amount, and speed of entry. This means in.

this instance comprises a hollow rod I00, adjustable in vertical slots IOI of the masonry structure 3. This rod is connected with a. cooling source by means of hose sections I02. This rod is mounted in plates I03 which are adjustably secured to plates I 04. The slots may be packed after adjustment of the pipe I00 has been made.

The temperature to which the coarse ore must be heated so that the resulting mixture'of the coarse and fine ore will have the required temperature must be carefully controlled, and the proportion of the mixture must be carefully controlled. And this is accomplished in part by the baflie element I00. When the ratio of the coarse to the fine ore is to be about five to'one, it is necessary to heat the coarse ore to a temperature of about 1270 F., if the desired temperature of the mixture is to be about 1100 F. If the ratio of coarse to fine is about four to one, the coarse ore must be heated to about 1310 F. If the ratio is three to one a temperature of about 1370 F. is necessary. The limitation as to temperature is due to the fact that the hot port casings are made of high temperature alloy steel which for long life should not be operatdcontinuously at a temperature above 1800 F. Further discussion regarding these factors appears below.

Reducing chamber Referring now.to Figures'l to 4 inclusive. An important feature of this invention is so to control the material that it moves downwardly uniformly' and without channeling, and so that thorough mixing of the two grades of ore occurs. Hereinbefore it has been shown that the coarse ore enters the heating chamber and in its descent therethrough passes between the exhaust ports and then the hot ports. At a point below the hot ports the finer ore is added. The resistance to the passage of gases through the coarse ore is such that for the quantity of hot gases required, a suction at the fan I6 of about 10 inchesof water is necessary. The contraction in the areas 53, 54 of the bottoms of the coarse ore bins, above referred to, is necessary to ly through the entire cross section of the heating zone and by having a uniform movement of the ore downward through the hot gases. To obtain mixing of the fine ore with the coarse the baffles are arranged not only to mix the coarse and-- fine but also to regulate the amount of fine ore that flows into the reduction chamber from the fine ore bins. The baflle element I controls j the rate of flow for mixing and the various bafi fles below this are adapted to mix the coarse and fine ores and at the same time give access of the I reducing gases to all of the ore particles.

Referring to Figures 1, 2 and 5, just below the i bafiies 9|, 92, 93,. and in the more restricted reducing chamber, is a centrally arranged baflle composed of three T-irons H0 arranged in 1 slightly spaced relation shown, and resting upon suitable mctal support III which have their ends 1 set into recess H2 as shown. Room for ex-pan- 1 pairs, one pair near each opposite wall'of the chamber, thus providing a central space H5.

The baille H6 of the lower of these two baflles are centrally arranged to provide lateral spaces 1 H1, as are provided by the arrangement of the irons H0. Below the baiile H6, are two moresets of baiiles H8 and H9. The upper set H8 for the-steam chamber 36. The lower end I40 of the casing of the steam chamber, see Figure 3, is disposed adjacent the rotary control plate 30, and the water in the tank 3I not only seals the bottom of the steam chamber 36 but also pro vides means for cooling the ore. The rotary feeder plate 30 is below the level of the water and as it rotates the hot ore slowly moves downwardly into the water thereby producing steam which escapes into the chamber 36.

Where the reducing gas used is natural gas or producer gas it may be introduced with or without preheating at pipe 32 under plate I25, and in such instances the. steam generated by quenching the ore is used for plant heatingor other purposes. However where the reducing gas is the vapor from oil, the steam may be used for such vaporization and is as shown in Figer baflies H8 and H9 are at right angles to the upper baflles.

The vertical flanges of the battles H8 and H9 are cut on a slant as shown at I2I. The action of these baiiies is diagrammatically indicated in Figure 13.

At the bottom of the reducing chamber-5 there occurs another restriction in area and for this I02, to receive a casing I03 having correspondi ingly slanted sides which lead into the pipe 39,

which in turn extends into the steam chamber i purpose the sides of the furnace are slanted as at 36. The reduction in furnace cross section area 1 is made so that the ore may be discharged through a small central opening.

Referring now to Figures 3 and 4 it will be observed that the casing I03 has mounted therein a plate I25 having openings I26 at opposite sides near the walls of the casing. Reducing gas f enters-through the pipe 32 and is delivered beneath the plate I25 whence it passes upwardly through the material which is flowing down-' wardly through. said openings I26. Depending from the plate I25 are two pairs of slanting respectively designated I26 and I29, which are slanted to conform to the slant of the f sides of the casing I03. The upper parts of j these baflies I28, I29 have openings respectively designated I 30 and I3I and the bottoms of the baille plates are connected by cross bars or .balfles respectively designated I33 and I34.

} Steam chamber After descending through the reducing chamj berthe ore enters the pipe 39 which delivers to the steam chamber 36.. This reduction in cross section of pipe 39 is desirable to prevent flow of 1 reducing gases into the cooling chamber and to control the flow of steam from the steam chamber into the reducing chamber.-

The lower 3 end of the steam chamber dips into the water of thequenching'tank 3|, the water beingmain tained at a constant level by afloat valve not shown.

As shown in Figure '13 the water forms a seal ures 1, 11 and 13, conducted through the pipe- 31 to an oil vaporized and condenser.

Since the steam is formed below the surface of'the water it passes upwardly through the ore to escape into the chamber 36 from which it is delivered to the top of the oil vaporizer 35,.as shown in ,Figure 11. In the vaporizer 35 the steam passes downwardly through pipes I46; and then meets the condensing water sprays issuing from the pipes 40. The condensate and spray water from chamber I 41 are drawn off and return through pipe I48 to the quenching tank 3|.

The water sprays condense all of thesteam leaving only the non-condensable gases consisting principally of air which was in solution in the water and the hydrogen formed by chemical reactions in the cooling zone. The quantities of these gases are small and they are pumped, see Figure 1, from the condenser through pipe H which is equipped with a valve I5I, to the explosion trap 42. The upper'end of the trap is connected by pipe 43 with the dust collector 22, and the suction is provided by a fan I6, through pipe 2I.

As shown in Figure 11, the pipes I46 pass through a chamber 164, into which the fuel oil to be'vaporized is delivered by pipe I55. The oil surrounds pipes I46 and after, being vaporized, ias2 delivered from the chamber I64 into the pipe Rotary feed control Referring now to Figures 1, 3, 4, 12 and 13,

particularly to Figures 1 and 3, it will be observed that the rotary feeder plate 30 is operated by shaft I through a worm drive I6I and shaft I62, the latter being driven by chain and smocket gear I63 from shaft I 64 which is in turn driven by pulley I65. The ore column is supported by the feed plate 30 in the manner shown in Figure 13, the rate of feed being controlled entirely by this plate, as follows:

The reduced and quenched ore is scraped from the plate 30 by a scraper indicated at I66 mounted on a cross beam I69 supported by the sides of the tank 3|. The ore .when scraped off falls into the tank'and sump I61 and is preferably removed therefrom by means of a conveyor of the type shown in my .Patent No. 1,449,216. Briefly such aconveyor includes a spiral scoop I 68 which delivers into a horizontal conveyor tube I69, the whole being' rotatably mounted. Tube I69 is arranged to be rotated from shaft I64 as shown in Figures-i and 12, by means of a sprocket chain drive I'll. .A clutch I is provided so that the feeder plate drive may be disconnected from the main drive shaft I64 when desired. Pulley IE is operated by any convenient power source means not illustrated, which is capable of being driven at variable speeds.

Operation I8 is operated at constant speed, change in the The overall scheme of the apparatus is best illustrated in Figure 13. The ore to be roasted is crushed to about three-fourths inch and then screened at four mesh. The coarser, or oversize material delivered into the coarse ore bins 50, 5|, and the finer or undersize delivered into the fine ore bins 52.' The three bins considered together may preferably have a. capacity of about'ten tons of ore in proportion of eight tons of coarse to two tons of fine. As the ore feeds down the fine ore bypasses the heating zone and does not enter the furnace proper until it reaches or almost reaches the reducing zone, whereupon it is introduced into the coarse ore below the hot ports 28. In an illustrative embodiment of the invention, the ore passes through the coarse ore bin at the rate of about eight and one-half tons per hour, and through the fine ore bin at the rate of one and one-half tons per hour, only the coarse ore being preheated. For best operating conditions, bins are never allowed to become empty.

The thermo-couples 33 which are placed at the entrance of the hot ports 28, permit temperature measurement of the gases entering the ports. For best results the temperature of the gases is not permitted to rise above 1800 F. The thermo-couple 45 in the cooling zone permits measurement of the temperature of the steam therein, which is approximately that of the temperature of the ore being discharged from the reducing chamber and for some operations this temperature may be maintained at about 1050 F. The cooling zone temperature is regulated by controlling the speed of the rotary feederat the bottom of the furnace, and as the temperature drops below 1050 F. the feeder is slowed down slightly, conversely as the temperature rises about 1050 F. the feeder speed is slightly increased. For preferred operation the temperature at the entrance to the hot ports 28 is maintained below 1800 F., the exact tempera- ,ture used being determined by the type of reducing agent used, and is regulated to maintain steam temperature in the steam chamber 38 at or below 1050 F. A pyrometer temperature indicator or recorder for each of the important temperatures throughout the furnace, together with an indicator or recorder for the number of revolutions of shaft I80 per unit of time of the feeder, are desirable adjuncts. Occasional readings of steam pressures and the pressure of the oil vapor or other reducing agent, enable the operator more closely to analyze o'perating'conditions.

The most important operational changesare due to changes in moisture content of the ore. As long as the moisture content is fairly constant, the furnace operates with a minimum of attention. v

The temperature of the gases from the combustion chamber 26, entering the hot ports 28 is dependent upon the amount of heat developed in the combustion chamber. Since the fan temperature of the gases in breeching 21 reflect changes in resistance to the'flow of the gases through the heating zone, and this change in this resistance is in turn due to changes in the size of the coarse. ore. The crude ore'is Ordinarily screened upon a 4-mesh vibrating screen or sometimes, if the ore is exceptionally wet it is necessary to use a 3 -mesh screen. When wet ore is encountered, more fine material passes through the heating zone with the coarse ore, thus increasing resistance to flow of gases with corresponding decrease in the amount of fuel that may be burned in the combustion chamber, and this occurs at a time when additional heat is necessary for evaporation of the additional water. Thus the amount of oil burned per hour is actually .less when the ore is wet than when dry. These facts are indicated by the curves in Figure 15, which show the changes in capacity and fuel consumption as the moisture changes in the ore. When the ore is wetter, due for example to rain, the first noticeable effect is the increase in temperature of the hot gases from the combustion chamber. This makes necessary an immediate reduction in the amount of oil being burned, in

order to reduce the temperature to normal. The next effect is a decrease in temperature of the steam, which indicates that the ore in the reduction chamber is cooler. To counteract this it is necessary that the feed rate be reduced until the temperature again reaches normal. If this is not done the quality of the roast decreases rapidly.

The eifect on the quality of the roast, of a change in temperature of the ore, is indicated by the temperature of thesteam, and is shown by the curves in Figure 16. These curves indicate that for a roasting efliciency of the temperature of the steam in this particular example should be about 1040 F.

Roasting efiiciency is defined as the percentage of iron oxide which is present as magnetite divided by. the total percentage of iron in the furnace product. As the steam temperature decreases, the efliciency falls off quite rapidly, and as it increases, the efiiciency increases slowly. From the above it is evident that the various adjustments in operation must be made because of changes in me moisture content of the ore. The adjustments are preferably automatically controlled by thermostatic devices (not shown) to regulate feeder speed, to maintain a constant steam temperature.

When the ore may conveniently be dried before screening and before feeding no substantial operating adjustments are necessary, and as an added advantage the fuel consumption per ton is materially reduced and the capacity of the furnace materially increased.

In its downward course the ore spreads against the sides 88 of the hood-like lower portion of the hopper. The coarse ore is divided as it passes the exhaust ports 25, and is again divided as it passes the hot ports 28, it being noted that the greater axes of these ports 25 and 28 are parallel. v

the same level.

'stantially prevent air leakage I ports.

'ducer gas or oil vapors.

the fine ore may be said to have been shunted around the heating zone, and it is only added to the coarse ore near the point'of entry of to cause each particle of ore, at any given level of the chambers, to move downwardly at approximately the same speed as other particles at The contraction in cross section at the bottoms of the coarse ore bins subdownwardly through the coarse ore bin into the exhaust By reducing this area the resistance to air passage is greatly increased and most of the air drawn from the furnace by the fan must accordingly enter the combustion chamber, pass into the hot ports, and then into the exhaust or cold ports.

\ It is preferable where high temperatures are used, to make the hot port casings, as well as most of the baffles, of special grades of alloy steel so that they will withstand the temperatures a used. The reducing zone and combustion zone are built of fire brick heavily insulated to prevent heat loss and the cooling zone is also in-. sulated to prevent loss of heat from the steam.

Where oil is used as a source of reducing vapors, about three gallons of oil per ton of ore fed for reduction is used. This oil is pumped into the vaporizer and is there converted to a vapor. Where other reducing agents such as natural gas or producer gas are used as the reducing agent a roughly equivalent volume of gas, based upon the B. t. u. value of the gas,

is used.

Approximately six. gallons of oil per ton of ore.

is fed for combustion iito chamber 26 where it i is burned in an ordinary oil burner (not shown) Where other fuels are used, the amount burned is equivalent in heat value to the amount of oil specified.

V The down-moving ore in the heating zone is traversed by hot gases which are the products of combustion from chamber 26, and which are being drawn upwardly through the hot ports 28. The resistance in this system is such that for the quantitiy of hot gases required, a suction at,

the fan of about ten inches of water is necessary.

After passing the hot ports, the ore passes downwardly into the reducing chamber where it meets the reducing gases, e. g. natural or pro- It will be notedthat the'oreinto the reducing zone. If the fine ore be computed when the proportion of coarse to fine ore is known.

In a representative embodiment of the invention the desired temperature of fine and coarse ore mixture is about 1100 F., when using oil temperature of about 1370 F. is necessary. The

best operating conditions are obtained when the ratio of coarse ore to fine ore is equal-to or greater than three to one, because of the difficulty of heating the coarse ore to sufliciently high temperature. The limitation of temperature is not ordinarily due to the melting or softening of the 'coarse ore since this normally does not occur below 2000? F., but is desirable because the hot port casings are constructed of high temperature alloy steel, which for long life should not be operated continuously at a temperature above 1800 F. When gas is used for reduction lower temperatures are maintained throughout the furnace.

The scheme of operations here illustrated for increasing the life of this part of the furnace is an important feature in the long life of the furnace. The maximum temperature of the productsof combustion entering the hot ports is limited by the materials used. Likewise the rate of the heat of transfer between the gas and ore is proportional to the ,diiT erence in temperature of gas and ore and decreases rapidly as the temperature of ore approaches the temperature of the products of combustion. Where it is desired to increase the temperature of the coarse ore, the time of contact between hot gases and'ore may be increased by either reducing the rate of feed (with consequent reduction in capacity),

' the exhaust ports is determined chiefly by the or a longer path of travel of gases through the ore may be secured (with consequent increase in the power required by the fan I8). The minimum temperature of the gases leaving amount of water in the ore and in the products of combustion, the water vapor being carried is not separated from the coarse before being passed through the heating zone, the power input to fan l6 must be'increased materially, and

at a. temperature of about 1882 F., and have a temperature of about 212 F. as they leave the exhaust ports 25. Lower temperatures are permissible when using natural or producer gas than when using vaporized oil as the reducing agent.

Because the fine ore is not heated directly, it is necessary to heat the coarse ore to a higher temperature than would otherwise be necessary merely for reduct'iomso that the coarse ore may give up part of its heat to the fine ore and yet still be sufliciently hot for rapid reduction.

The temperature to which the coarse ore must be heated so that the resulting mixture of coarse and fine will have the required temperature, may

. stantial extent through the fine ore, the amount cause flame in the hot port casings may cause 1 away as vapor. Since the amount of water carried by the ore may vary due to precipitation, the exhaust ports are normally placed about 18 inches above the hot ports in order to maintain the temperature of the exhaust. gases at approximately 200 F. At this temperature the carrying power of gas for water vapor is so large that even abnormal quantities of moisture are carried off without difiiculty.

The finer ore which bypasses the heating zone passes over and around the hot ports and receives some heat from them by direct contact, but since gases cannot pass upwardly to anysubof heat which it absorbs is usually little more than sufficient to vaporize the moisture of the fine ore.

The combustion chamber which supplies 'the hot gases to the hot ports is designed for the combustion of oil, but may also be fitted for the combustion of natural or artificial gas or coal. In any design,- whether the fuel be oil, coalor gas, suflicient combustion spaceis provided in order that flames do not enter the hot port casings. This is an important consideration beoverheating and rapid deterioration of the alloy steel. As a safeguard against overheating thermo-couples 33 are placed in the entrance of the hot ports, and the rate of combustion is so regulated that the temperature of the hot ports is 1800 F., or less at all times. It is obvious that for satisfactory operation and this can best beaccomplished by having a uniform flow of gas upwardly through the entire cross section of the heating zone and a uniform movement of the ore downwardly through the hot gases.

The means for securing these uniformities of movement of the ore and heating gases are important aspects of the invention. Whether or not the movement of the ore at any of these points is uniform depends uponthe movement of the ore below the heating zone. It was found dwirable for structural as well as metallurgical reasons to reduce the cross sectional area of the furnace below the heating zone-since this increases the velocity of the reduced gases upwardly through the ore and simplifies the problem of uniformly mixing the flne ore with the coarse.

The baflling herei'n illustrated and described produces uniform mixing and movement of the ore through the furnace and uniform contact with the reducing gases notwithstanding the restriction of the furnace area below the heating zone.

As shown in Figure 3 the fuel pipe 32 delivers reducing gas 01 vapors beneath the plate I25 and the gas passes upwardly through openings best shown in Figure 13, have the effect of mix- 7 ing the coarse and fine ore and at the same time permit the reducing gases to reach to all of the ore particles. The open spaces below each of the bafiies serves to equalize the gas pressure and produces desired directions of, flow since the gases thus tend to flow from one open space to the next above. Beneath the baiile III) and, if need be beneath the bafile II6, are placed draw-offpipes I22, I23, for the removal of any desired proportion of the reducing gases traveling upwardly. This for the purpose of preventing such gases from reaching the top of the reducing chamber, that is, reaching the point at which the fine ore is introduced into the coarse whereby to prevent interference with temperature re ulation at this point for the purposes previously mentioned. The unused reducing gases thus removed may be used as fuel in the system, this being accomplished 'by suction apparatus, not illustrated, for removing the gases and delivering them to the furnace 26.

As explained above the baflles are arranged so as not only to mix the coarse and fine ore but also to regulate the amount of fine ore which flows into the reduction chamber from the fine ore bin. The various baflles in the reducing chamber are designed to mix the coarse and flne ores, and at the same time give the reducing gases access to all of the ore particles,

Near the bottom of the reducing chamber, reducing gas such as natural gas, producer gas or oil vapor is forced into the furnace and passes upwardly through the already heated ore thereby causing a, chemical reduction change from hematite to magnetite to take place. The reducing gas may-be formed, as before stated, by vaporized fuel oil in a vaporizer heated by steam from the steam chamber. .In this instance the vaporizer, see Figure 11, is somewhat similar to a fire tube boiler, and the high temperature steam passes downwardly through two inch pipes which are surrounded by the oil to be vaporized. The temperature of the steam is somewhat above 1000 F. and the boiling point of the oil used, is about 600 F. In the vaporizer the oil is not only vaporized but the vapor is superheated to a temperature of about 900 F.- The oil is pumped into the vaporizer at a rate that produces the required flow of reducing gas, and the oil assumes the level ,in the vaporizer depending upon the amount and temperature of the steam being produced in the steam chamber.

The reducing agent itself can be improved by converting the hydrocarbons into hydrogen and carbon monoxide. No attempt is made to crack the oil in the vaporizer, but upon its entry into the reducing chamber in contact with the iron oxide, reactions occur that produce principally methane, carbon, carbon monoxide, and hydrogen, the two latter being the active reducing agents. The carbon is discharged from the furnace with ore and is lost and the methane passes upwardly through the reducing chamber. In the event unused methane reaches the hot ports, combustion will there take place with consequent overheating. In order to overcome this difficulty, it is desirable to withdraw the unconsumed reducing gases at the top of the reduction chamber and for economy they may burned in the combustion chamber 26.

After descending through the reducing zone 5, the ore enters the cooling zone through pipe.39, and then enters a water bath. As before stated the feed of the ore is controlled by a revolving plate 30 upon which the charge rests. As this plate revolves the hot ore moves slowly downwardly into the water. The water level is several inches above thebottom of the hopper so that the ore does not fall into the water but passes into it gradually, as the ore is withdrawn by the action of the discharge plate. Contact between ore and'water produces a considerable quantity of steam which is collected and discharged through the steam pipe 31, to the vaporizer or to any other desired auxiliary. The temperature of the steam is 1000 to 1100 F. which is about the temperature of the ore of the cooling zone. Therefore, a considerable quantity of cooling of the ore is accomplished by superheating the steam, and the heat thereby stored may be utilized for heating, vaporizing oil, drying ore or any other purpose;

The thermo-couple in the steam outlet from the cooling chamber directly indicates the temperature of the ore being discharged and this is one of the major operating controls. The reduced ore should be cooled below a temperature of 212 F. before it contacts the air, to prevent reoxidation of the hematite.

To prevent reducing gases from forcing downwardly into the steam chamber, it is desirable to maintain the steam pressure equal to or greater than the pressure ofthe gases in the reducing chamber. The presence of a limited amount of water. By balancing the pressure of the steam.

so that only a small amount of steam will move upwardly into the reducing chamber, the reducing gas will be prevented from flowing out into the cooling zone. It is not necessary to maintain the pressures exactly equal as a slight upwardseepage of steam is not objectionable.

Upon leaving the oil vaporizer (where used), the steam enters the condenser where it meets several water sprays whereupon the steam is condensed. The pressure in the steam chamber 36 is maintained constant by maintaining the pressure in the condenser constant at about oneand one-half inches of water less than that in the steamchamber.v Only non-condensable gases which consist of air in solution in water and such hydrogen as has been formed by chemical reactions in the cooling chamber remain, and since the quantity of these non-condensable gases is small they may be drawn from the condenser by fan l6 which communicates with the condenser by pipe 4 3, tube 42, pipe 4| and valve I5l. -By controlling the suction of the fan l6 by means of valve Hi, the pressure of steam in the cooling chamber may be adjusted. 'The noncondensabl gases may form an explosive mixture and they are'therefore passed through the explosion trap 42. e

The steam produced in the cooling zone may be usedfor any desired purposes thus conserving heat, since the steam contains about two-thirds of the heat absorbed by the ore in the heating,

zone. In a representative embodiment of the present invention approximately two hundred pounds'of steam at a temperature of 1000 F. is produced per ton of ore fed to the furnace. It is at a pressure of about one-fourth of an inch of 'water and contains considerable dust, part of which is as coarse as twenty mesh. This dust is all in the form of magnetite and for economy is returned to the quenching tank with the water from the condenser. Obviously the dust must be removed when the steam is used for some purposes.

The temperature of operation of th furnace may be controlled so as to obtain a maximum production with a minimum of deterioration of the various alloy steel castings, and baflles of the furnace. The castings and baiiies are so arranged as to allow for ample expansion, and this arrangement combined with the novel control in many instances permits at least 20,000 hours of continuous operation without a shut down for repairs.

Undernormal conditions the operation of the furnace is simple. Thermo-couples placed at the entrances to the hot port casings indicate the temperature of the gases from the combustion chamber, this temperature being maintained at about 1800 F. when oil vapor is used for reducing and at even .lower temperatures when natural or other gases are used for reduction.

A thermo-coupl in the cooling chamber indicatesthetemperature of the steam being produced. In a representative adjustment, in one operation, this temperature is found to be about 1050 F'., to produce properly roasted ore. The temperature was maintained by controlling the speed of the rotation of the feeder 30, and as the temperature dropped below 1050 F. the feeder speed was slightly decreased. As the temperature increased above 1050" F. the speed of the feeder is slightly increased. The chief duty of the operator is to maintain the temperature at the entrance of the ports'at about 1800 F. or any selected temperature depending upon the reducing agent used and the proportion of coarse to fine ore used, and to operate the feeder at the proper rate of speed to maintain a steam temperature of about 1050 F.

, Fuel consumption per ton increases as the ore becomes more moist, This change, however, has practically no effect on the metallurgical results secured in the magnetic concentration plant, for when suitable adjustments are rmade the grade of concentrate, the percent of weight recovery, and the percent of iron recovery remain practically constant. For example: When\the ore is exceptionally dry, containing only about 6.2% of moisture, the temperature of steam may be 1087" F. indicating that the feed rate would be increased above nine tons per hour.

I claim as my invention:

1. A shaft type roasting furnace comprising means at the top of the shaft for separately receiving coarse and fin ore, a heating zone through which the coarse ore passes and through which the heating gases are drawn, therebyheating the coarse ore, a conduit for carrying the fine ore by the heating zone without substantial heating, a reacting zone on which'the hot coarse ore, the cool fine ore, and the reacting gases are moxed, a cooling zone in which the ore meets a cooling agent, and discharge means so arranged that the entire shaft of the furnace is kept filled with ore at all times and means in the interior of the furnace so arranged that the ore particles pass through the furnace at approximately a uniform rate. v

2. An apparatus for reducing ore comprising a structure providing a vertical shaft having, a heating zone in the upper portion, a reducing zone below the heating zone, means above the heating zone for selectively feeding relatively coarse and fine ores to said heating zone and for causing the finer ore to be added to the coarser ore in the lower portion of said heating zone, means for introducing heated gases into the lower portion of the heating zon in the neighborhood of the point of mixture of said coarse and fine ore, means for causing the introduced gases to bedrawn upwardly through the charge in the heating zone, means for introducing vaporized reducing gases into the lower portion of the reducing zone, baflling means in the reducing zone for mixing of the coarse and fine ores as it travels, a cooling chamber below the reducing zone into which the reduced ore is delivered, a quenching tank into which the reduced ore is discharged, means in the quenching tank in part supporting the charg and regulating the speed of its downward travel, and means for removing the quenched cooled reduced ore from said reducing tank.

3. An apparatus for reducing hematite ore to magnetite ore comprising a structure providing an upright shaft, said shaft having a heating zone in the upper portion, a reducing zone below the heating zone, means positioned above the coarse and fine o e into said zone, means for introducing prod ts of combustion into the lower portion of the heating zone, suction means for causing such products of combustion to travel upwardly through the cm in the heating zone, a passage by which the feeding means introduces fine ore only into the bottom portion of the heating zone and in the neighborhood of entry of said gases of combustion such introduction taking place near the upper portion of the reducing zone, means for introducing vaporized reducing agents in the lower portion of the reducing zone, bafliing means in the reducing zone aiding in mixing of the coarse and fine ores as they descend therethrough, a cooling chamber below the reducing zone having water therein, and feeding means submerged in the water and supporting the column of ore and acting to, regulate the heating zone Z? adapted to separately feed I down travel of the charge.

4. An ore treatingfurnace having, a steam chamber, a reducing chamber delivering to said steam chamber, mixing and flow control bafiies within said reducing chamber, a heating chamber delivering to said reducing chamber, hot ports in the heating chamber, exhaust ports, means by which coarse and fine ore is separately delivered to a point adjacent said reducing chamber, and so that the coarse orev is heated by passage through said heating chamber, means creating suction in the exhaust and hot ports, means for supplying heat to said hot ports, a quenching tank to which ore is delivered from said reducing chamber and having water therein which seals the bottom of the steam chamber, a feeder submerged in the water supporting and controlling down travel of the ore and means for delivering reducing agents into said reducingchamber. v

5. An ore treating furnace having, a steam chamber, a reducing chamber delivering to said steam chamber, mixing and flow control baiiles within said reducing chamber, a heating chamber above and delivering to the reducing chamber, hot ports in the heating chamber, exhaust ports in said chamber above said hot ports, means by which coarse and fine ore is separately delivered to "aid heating chamber to a point below said hot ports, and so that the coarse ore is heated by passage through said heating chamber, means creating suction in the exhaust and hot ports, means for supplying heat to-said hot ports, a quenching tank to which ore is delivered from said reducing chamber, and having. water therein which seals the bottom of the steam chamtherein which seals the bottom of the steam chamber, a feeder submerged in the water and -supporting and controlling down travel of the ore, means for delivering vaporized oil into said reducing chamber, and means by which the oil is vaporized by steam from said steam chamber.

7. An ore treating furnace having, a steam chamber, an upright reducing chamber delivering downwardly to the steam chamber, baflies within said reducing chamber arranged to obtain uniform down movement of the ore, a heating chamber of larger cross-sectional area than that of the ber, a feeder submerged in the water and which supports and controls down travel of the ore said reducing chamber.-

6. An ore treating furnace having, a steam chamber, a reducing chamber delivering "downwardly to said steam chamber, mixing and flow control banies within said reducing chamber, a heating chamber delivering downwardly to said reducing chamber, hot ports near the bottom of said heating chamber, exhaust ports in said chamber above said hot ports, means by which coarse and fine ore is separately delivered to said heating chamber to a point adjacent and below said hot ports, and so that the coarse ore is heated by passage through said heating chamber, means creating suction in the exhaust and hot ports, means for supplying heatto said hot ports, a quenching tank to which ore is delivered reducing chamber and delivering downwardly thereinto the latter, baiiies within said heating chamber slanting inwardly and downwardly toward said reducing chamber, hot ports adjacent and immediately above said baiiles, exhaust ports in said chamber above said hot ports, means by which coarse and fine ore is separately delivered, to become confluent at a point adjacent said slanting bailies andbelow said hot ports, and so that products of combustion pass only through the coarse ore, means creating suction in the exhaust and hot ports, means for supplying heat to said hot ports, a quenching tank to which orev is delivered from said reducing chamber, and having water therein which seals the bottom of said steam chamber, a rotary feeder submerged in the water and which supports and controls down travel of the ore, means 4 for delivering vaporized oil into said reducing chamber at the bottom thereof, and means by which the oil is vaporized by steam-from said steam chamber.

8. An ore treating furnace having tom a steam chamber, a reducing chamber delivering downwardly to the steam chamber through a constricted orifice, baiiies arranged in horizontal sets within said reducing chamber, each set comprising a plurality of parallel bars certain of the long axes of the bars of sets extending at right angles to the long axes of the bars of other sets, a heating chamber of larger crosssectional area than that of the reducing chamber and delivering downwardly thereinto, slanting baflies arranged at the bottom of said heating chamber and leading inwardly and downwardly toward said reducing chamber, hot ports adjacent and immediately above said last mentioned baflles, exhaust ports in said chamber above said hot ports, a fine ore hopper delivering to said heating chamber to a point adjacent said slanting baffles and below said hot ports, and a pair of hoppers which deliver coarse ore into the top of said reducing chamber above said exhaust ports, means creating suction in said exhaust and hot ports, means for supply n heat 110 said hot ports, a quenching tank to which ore is delivered from said reducing chamber, and having water therein which seals the bottom of said steam chamber, arotary feeder and which supports and controls down-travel of the ore, means for delivering vaporized oil into said reducing chamher at the bottom thereof, and means by which the oil is vaporized by steam from said steam chamber.

9. An ore handling device comprising a vertical container having a vertical space therein for movement of ore in a solid column downwardly therethrough, means for introducing relatively coarse ore at one part of said space, means for introducing relatively fine ore into the coarse ore as it moves downwardly through a lower part of said space, and means for intermixing the relatively coarse and relatively fine ore while in a from said reducing chamber, and having water solid column moving downwardly through said at the bottively fine ore into the space including a plurality oi long relatively narrow baiilemembers traversing said vertical space in the path of movement of the solid column of ores below the point 01' introduction oi the relaand means for removing the column of ore from a lower part of said space.

10. An ore treating furnace comprising a vertical container having vertical space therein for 11. An are treating furnace comprising a vertical container having a vertical space therein for movement of ore in a solid column downmovem'ent of are in a solid column downwardly the solid column while the column is moving below the place of introduction 01' go downwardly fine ore.

wardly therethrough, means for moving relatively coarse and relatively fine ores in separated solid columns downwardly through a part of said 1' space, means for heating the relatively coarse ore as it thus moves downwardly while separated from the relatively fine ore, and means for admixing the thus heated relatively coarse ore and relatively flne ore in a lower portion of said space while moving downwardly in a solid column therethrough.

12. The combination of claim 11 wherein the means for admixing comprises a plurality of narrow bailies set some above others and extending across the space.

I EDWARD W. DAVIS.

CERTIFICATE OF CORRECTION. Patent No. 2,257,110. September 0, 191,1.

EDWARD w. DAVIS.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page '8, second column, line 57, claim 1, for the word "on" read -inline 59, same claim,- for "moxed" read -mixed-; and that the said Letters Patent should be read with this correction therein that the same may conform to the rec- 0rd of the case in the Patent Office.

Signed and sealed this 25th day of November, A. D. 19M

Henry Van Arsdale (Seal) I Acting Commissioner of Patents, 

